Biocatalytic carbon nanotube paper: a 'one-pot' route for fabrication of enzyme-immobilized membranes for organophosphate bioremediation

Recent world events have demonstrated the critical need for facile and miniaturized bioremediation technologies for organophosphates (OPs). These compounds are among the most toxic substances synthesized to date and are used as pesticides and nerve agents. Biotechnological methods based on the use of organophosphate hydrolase (OPH) for detoxification of OPs have drawn significant attention. This work presents a new 'one-pot' methodology for a rapid and straightforward fabrication of enzymatically active carbon nanotube (CNT) paper for OP bioremediation. Carboxylated CNTs are ultrasonically dispersed in an aqueous surfactant solution followed by a microfiltration process to generate a paper-like membrane, which is assembled from entangled nanotubes. Herein, OPH conjugation to the CNTs is carried out by carbodiimide chemistry during the microfiltration process. Successful covalent immobilization of the enzyme onto the nanotube surface is confirmed by cryo-transmission electron microscopy and infrared spectroscopy. To study the potential of this platform for OP bioremediation, an aqueous solution of methyl paraoxon (used as a model OP) is filtered with the resulting OPH-CNT membranes. A significant decrease of methyl paraoxon concentration is achieved, which is ascribed to its in situ hydrolysis by the immobilized OPH during the filtration process. These thin membranes allow many subsequent filtration cycles to be performed, while maintaining their enzymatic activity, owing to the unique combination of the mechanically robust CNT scaffold and high OPH loading. This study presents a new generic approach for the design of bioactive paper-like scaffolds, which can be rationally tailored for a variety of applications.